A definite need has long existed for an efficient, economical apparatus to dampen the printing plates on lithographic printing presses and particularly rotary, lithographic newspaper presses. Such apparatus preferably should avoid contact between the dampening fluid supply elements and any ink carrying surface to thereby preclude or at least minimize the contamination with ink of the supply elements and/or the fluid in the dampening system.
Various types of dampening mechanisms have been used in the past on rotary newspaper presses, but without complete success. Continuous duty type dampeners that are used widely on commercial presses, for example, have proved to be unsatisfactory on newspaper presses. This is due primarily to their inability to consistently supply sufficient water to the plate in order to compensate for the loss thereof due to the absorptive nature of newsprint stock and the normal high running speed of such presses.
Brush type dampeners also have failed to satisfy the requirements. These devices are subject to contamination, premature wear, inconsistency in the amount of water transferred and they tend to project or spray relatively large droplets which are clearly discernable as water spots in the printed products. Other known types of spray dampeners also have failed to gain commercial acceptance for various reasons such as the large droplet size, their inability to provide uniform coverage, lack of efficient lateral controls and/or clogging due to the additives required in the dampening solution.